1. Field of the Invention
The present invention relates to the application of inorganic oxide porous materials used for catalysts, adsorbents or the like, more specifically mesostructured materials having a controlled mesopore orientation and a preparation method thereof.
2. Related Background Art
Porous materials are widely utilized for various purposes such as adsorption and separation. According to IUPAC, porous materials are classified into three classes based on the pore size, i.e., microporous, mesoporous and macroporous materials having the pore sizes of not more than 2 mm, 2 to 50 nm and not less than 50 nm, respectively. In the microporous materials, metal phosphates, zeolite, such as natural aluminosilicates and synthetic aluminosilicates and the like, are known. These materials are utilized for selective adsorption, a shape-specific catalytic reaction and a molecular size reactor by exploiting their pore size.
Since the maximum pore size of the reported microporous crystals is about 1.5 nm, the synthesis of solids having a larger pore size is an important issue for conducting adsorption and reaction with bulky compounds, which cannot be adsorbed into the micropores. Although silica gel, pillared clay or the like have been known as materials having such larger pores, the pore size distributes in a wide range and control of the pore size has been a problem.
In such a background, synthesis of the mesoporous silica having mesopores of the same size arranged in a honeycomb-like arrangement have been achieved almost simultaneously by two different methods. Namely, one mesoporous silica called MCM-41 was synthesized by hydrolyzing silicon alkoxide in the presence of surfactants (Nature, vol. 359, p. 710), and the other material called FSM-16 was synthesized by intercalating alkyl ammonium between layers of kanemite, a layered polysilicate (Journal of Chemical Society Chemical Communications, vol. 1993, p. 680). In both methods, it is considered that the surfactant assembly acts as a structure-directing agent of mesostructured silica. These substances are not only extremely useful as catalysts for bulky compounds, which cannot enter the zeolite pores, but are also applicable as functional materials such as optical and electrical materials.
When applying the mesoporous materials having such a regular porous structure to the field of functional materials other than catalysts, the technology for retaining these materials uniformly on a substrate is important.
There are several methods for preparing a mesoporous thin film on a substrate, such as a spin coating method as described in Chemical Communications vol. 1996, p. 1149; a dip coating method as described in Nature, vol. 389, p. 364; a method based on the heterogeneous nucleation and growth on a solid surface as described in Nature, vol. 379, p. 703 or the like.